Police in Jamaica said a man, a woman, a baby boy and his five-year-old sister, were driving along a flooded rural road in the south-west of the island when a surge of water pushed them over a cliff.
On the coast of Mexico, Francisco Alor, the Mayor of Cancun, said: "We have very little hope this will change course. This hurricane is coming with the same force as Gilbert." That hurricane in 1988 killed 300 people in Mexico.
Officials began the evacuation of 85,000 people across more than 100 miles (160km) of coastline and ordered more than 30,000 tourists in Cancun to move. The state oil company, Petroleos Mexicanos, evacuated offshore platforms of 15,000 workers.
Emily's winds strengthened on Saturday night to near 155mph (250kph). That could make it the strongest storm on the Saffir-Simpson scale, a Category 5 hurricane. Dave Roberts, a meteorologist said it was the strongest storm to form this early in the Atlantic season since record-keeping began in 1860.
Wind gusts kicked waves 8ft high and bent palm trees double in Kingston, Jamaica's capital. Torrential rains drenched the south coast and washed away at least three houses. Downed power poles and piles of other storm debris blocked the seaside highway to Kingston's international airport and other roads.
Late yesterday Emily was centred 165 miles south-west of Grand Cayman Island and 250 miles east-south-east of Mexico's resort island Cozumel. The storm was moving west-north-west. Hurricane winds extended 60 miles and tropical storm force winds a further 150 miles.
Emily was expected to strike Mexico's resort-packed Yucatan peninsula late last night or early today. After that, if Emily remains on track, it is expected to lose strength moving overland but regain dangerous energy in warm waters over the Gulf of Mexico. The hurricane is likely to make landfall again on Wednesday, near the US-Mexico border, between north-eastern Mexico and southern Texas.
Long lines of tourists choked Cancun airport yesterday and hundreds of buses were moving others to safer areas inland.
"The locals seem pretty nonchalant about it," said Becky Hart, 29, a school teacher from Madera, California, as she waited to board a plane. "Then at the hotel they started chopping down the coconuts from the trees and moving people from the top floors. People were boarding up windows."
There are about 100 British guests at Riu Palace Las Americas hotel in Cancun. Valera Martinez, a receptionist, said: "We have to start evacuating peopleand busing them to our hotel downtown, away from the coast. We have more than 800 people to move before the weather worsens."
Emily is the fifth named storm and second major hurricane of the season. Tropical Storm Cindy and Hurricane Dennis tore through the Caribbean during the past two weeks, killing at least 20 people.